Anechoic visco-thermal liner

Abstract

A liner assembly includes a plurality of aligned passages providing a large open area combined with openings much smaller than a length of the passages. The plurality of passages are disposed parallel with each other and include an opening transverse to incident sound waves. The passages are separated by walls and are blocked at an end distal from the openings. Sound waves incident on a face of the liner enter the passages and are dissipated by viscous losses. Sound energy is further dissipated as thermal energy to the walls of the passages. The long narrow passages provide the desired visco-thermal losses for sound energy in a broad frequency range.

Description

BACKGROUND OF THE INVENTION[0001]This invention generally relates to an acoustic liner. More particularly, this invention relates to an acoustic liner for minimizing reflection of sound from the acoustic liner face.[0002]Conventional nacelle liners include a noise attenuating structure covered by a face sheet including a plurality of openings. The openings communicate noise and acoustic energy through to the noise attenuating structure where the acoustic energy is dissipated. The face sheet includes an open area provided by the plurality of openings that is generally less than 20% of the total area of the face sheet. The open area provided by openings within the face sheet is configured to attenuate the most undesirable noise frequencies. The limited and tailored open area prevents sound energy of some frequencies from being dissipated and instead reflects that sound energy back into the nacelle. Greater open area can provide improvements to the range of noise frequencies that can b...

AI Technical Summary

Benefits of technology

[0009]The width of the openings is very small relative to the length of the passage and is combined with many other passages to provide a relatively large opening area on the face of the liner and to provide a large surface area within the liner to maximize the dissipation of the sound energy within the liner. The opening area of the face is greater than 80%. The large opening area provides a substantially anechoic liner that reflects substantially little sound. The reduction in the amount of noise energy that is reflected from the face provides substantial improvements in the visco-thermal dissipation of noise energy.

[0010]Accordingly, an example liner assembly according to this invention provides increased noise attenuation across a broader frequency range than conventionally configured acoustic liners.

Problems solved by technology

Disadvantageously, there is a practical limit to the number and size of the openings that can be provided within a face sheet.

Further, although possible to tune the liner to attenuate noise of certain frequencies, such tailoring results in a limit to the range of frequencies that can be effectively attenuated.

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